What Are Bored Piles?

A bored pile foundation is a type of reinforced concrete foundation that supports structures with heavy vertical loads. Unlike driven precast piles, bored piles are cast-in-place using concrete on site.

The rotary piling technique is performed by drilling through a temporary casing to the designed depth, using an auger, eliminating any spoils. The casing supports the pile through to the ground until the required depth is achieved, the auger is then removed, and the concrete is poured in situ to form the bored pile.

This video demonstrates the installation of Kelly Bored Piles using a large bored piling rig:

The excavation of the auger bored piles is done using a large drill driven by a heavy drill motor. The stability of the borehole is upheld by placing steel casings, which are driven into the soil using a telescopic Kelly bar. When casting concrete around the pile, the steel casings are recovered.

Both bored piling and screw piling are deep foundation solutions, but they have some differences. While bored piling involves drilling a borehole into the ground through a temporary casing and filling it with concrete, screw piling is performed by driving steel screws with helices on the outside into the soil. The screw piles are designed without having to remove any soil.

Rotary bored piling is one of the most widely used bored pile techniques, particularly suited for sites where large diameters or deep penetration into hard strata are required. It offers several distinct advantages, making it one of the most versatile piling methods for challenging ground conditions.

This method can be installed in the vast majority of soil types, including dense strata and rock, and is ideally suited where high structural load capacity is required. Using specialist drilling tools such as buckets, augers, and core barrels, rotary bored piling can penetrate man-made obstructions and create rock sockets for increased end-bearing capacity.

It also achieves tight tolerances near boundaries, making it suitable for restricted urban sites and basement works. In addition, rotary bored piles can incorporate advanced monitoring systems, such as fibre-optic instrumentation, allowing for real-time performance assessment and quality control throughout the construction process.

Bored piles are known as large diameter piles if they have a diameter of 600 mm or more. Small diameter bored piles are less than 600 mm and are sometimes placed in groups under a common pile cap to support heavy loads. [2]

The bearing capacity of large diameter piles can be increased by under-reaming the shaft at the base. This is achieved by an expanding cutting tool which cuts a conical-shaped base up to three times the diameter of the main shaft.